The universal cell organelle facilitating protein biosynthesis is the ribosome. A typical bacterial ribosome is of molecular weight of 2.3 MD and contains 57-73 different proteins and 3 RNA chains with 450 nucleotides. Crystals diffracting best to 1.9 _ were grown from ribosomal particles of halophilic and thermophilic bacteria. Data were collected at cryogenic temperatures from flash frozen crystals at F1/CHESS, using the 2K-CCD Princeton detector (rotation ranges of 0.1-0.4 degrees, 60-10 seconds each). The so far evaluated data show Rmerge(I)=6-13% for 80-90% completeness. A significant decay was observed after collecting 5-8 degrees, introducing sever difficulties in constructing full data sets because of the low level of isomorphism of the ribosomal crystals. This problem was partially overcome by using beam with small dimension and irradiating the crystals part by part, until each of them showed substantial decay. In favorable cases, it was possible to collect 15-20 degrees from one crystal. Heavy atom derivatization was performed by soaking crystals in solution of heteropolyaniones. In general the soaked crystals diffracted to almost the same resolution as the native ones, but not always could we collect all the data, due to restrictions in beam time. The low degree of isomorphism required the collection a few data sets until the suitable candidates for the construction of difference Patterson maps were found. Preliminary phases at intermediate resolution were determined. These were used for calculating electron density maps which showed features with the shape and the size expected for the corresponding particle. In preparation for MAD phasing, data were collected from crystals soaked in solution containing K14NaP5W30O110 at three wave-lengths, two of them close to the absorption edge of this particular W cluster. Measurable anomalous signals have been detected. However, their usefulness in phasing remains to be seen, and is being currently assessed.